Gluing Living Bone Using a Biomimetic Bioadhesive: From Initial Cut to Final Healing

Abstract

Osteoporotic fractures are a growing issue due to the increasing incidence of osteoporosis worldwide. High reoperation rates in osteoporotic fractures call for investigation into new methods in improving fixation of osteoporotic bones. In the present study, the strength of a recently developed bone bioadhesive, OsStic^tm, was evaluated in vivo using a novel bone core assay in a murine animal model at 0, 3, 7, 14, 28, and 42 days. Histology and micro-CT were obtained at all time points, and the mean peak pull-out force was assessed on days 0-28. The adhesive provided immediate fixation to the bone core. The mean peak bone core pull-out force gradually decreased from 6.09 N (σ 1.77 N) at day 0 to a minimum of 3.09 N (σ 1.08 N) at day 7, recovering to 6.37 N (σ 4.18 N) by day 28. The corresponding fibrin (Tisseel) control mean peak bone core pull-out characteristic was 0.27 N (σ 0.27 N) at day 0, with an abrupt increase from 0.37 N (σ 0.28) at day 3, 6.39 N (σ 5.09 N) at day 7, and continuing to increase to 11.34 N (σ 6.5 N) by day 28. The bone cores failed either through core pull-out or by the cancellous part of the core fracturing. Overall, the adhesive does not interrupt healing with pathological changes or rapid resorption. Initially, the adhesive bonded the bone core to the femur, and over time, the adhesive was replaced by a vascularised bone of equivalent quality and quantity to the original bone. At the 42 day time point, 70% of the adhesive in the cancellous compartment and 50% in the cortical compartment had been replaced. The adhesive outwith the bone shell was metabolized by cells that are only removing the material excess with no ectopic bone formation. It is concluded that the adhesive is not a physical and biochemical barrier as the bone heals through the adhesive and is replaced by a normal bone tissue. This adhesive composition meets many of the clinical unmet needs expressed in the literature, and may, after further preclinical assessments, have potential in the repair of bone and osteochondral fragments.

Keywords: biomechanical model; biomimetic; bone adhesive; calcium phosphate cement (CPC); fracture healing; orthobiologic; phosphoserine.

FIGURE 1

Ex vivo and in vivo methods for the bone core osteotomy and gluing procedure. Ex vivo: (A) bone core trephine tool, (B) murine femur extraction screw placed and bone core cut, (C) removal of bone core, (D) placing adhesive in the osteotomy, and (E) bone core replaced and glued in place. In vivo: (F) blood flow after bone core removal, (G) additional adhesive layer at the bottom of bone core osteotomy, and (H) bone core replaced and glued in place.

FIGURE 2

(A) Tensile test setup and (B) Detail of loading jig.

FIGURE 3

Adhesive at 42 days: (A) overview of the bone core, (B) active resorption of adhesive excess with vessels visible inside resorption cavities, (C) resorption of the bone core, (D) interface between core (to the left) and host living cortical bone, BMUs throughout the material, and (E) evidence of adhesive material remodeling, lamellar trabeculae.

FIGURE 4

Micro-CT images at weeks 0 and 6; 42 day histology shows complete bone layer fully covering the adhesive material following the cortical line. Material is fully integrated in the newly formed bone showing early formation of the osteonal structure.

FIGURE 5

Mean peak pull-out force for the OsStic adhesive with representative force displacement curves at each time point (selected a curve closest to the mppf).

FIGURE 6

Mean peak pull-out force for the Tisseel control with representative force displacement curves at each time point (selected a curve closest to the mppf). The OsStic curve is included for comparison.

FIGURE 7

Average stiffness taken from load displacement tests for each material at each time point.

FIGURE 8

OsStic adhesive and Tisseel bone core failure modes.

FIGURE 9

Under the core volume of interest mean value at each time point (UC VOI) versus mppf for the OsStic adhesive.

FIGURE 10

Schematic illustration of bone core loading during pull-out.

FIGURE 11

A typical adhesive bone core fracture surface and a section to illustrate a typical bone core trabecular cross section.

FIGURE 12

Implant stability dip during healing: (A) screw pull-out in the cancellous bone, (B) dental implant, and (C) soft tissue wound healing.

FIGURE 13

Hypothesis for the time course of tensile strength between two osseochondral fragments.